Steel and non-ferrous metals are being smelted throughout the world in circular furnaces with steel containment shells. Some of these employ panel type stave coolers that completely line the interior walls to cool refractory bricks mounted to their hot faces. Their individual cooling actions are delivered by liquid coolants that circulate inside each stave cooler with piping that passes through penetrations of the steel containment shells to access an external heat exchanger. Each penetration of the steel containment shell requires reliable welds and seals to keep the hazardous process gases both inside the furnace and away from its operating personnel.
Production rates exceeding three tons of hot metal per cubic meter of working volume per day are now being reached with modern blast furnaces. This was made possible by using improved burden materials, better burden distribution techniques, tighter process controls, very high hot-blast temperatures, oxygen enrichment technology, pulverized-coal injection, and natural gas fuel enrichment. All of which result in much higher average heat loads and fluctuations that land on the stave coolers mounted inside the steel containment shells of up-to-date blast furnaces.
Integrated steelworks use blast furnaces to supply themselves the pig iron they use to make steel. The large gains being made in furnace-productivity have also placed overwhelming demands on cooling system capacities. The liquid-cooled stave coolers in blast furnaces first developed in the late 1960's became inadequate. High conductivity copper stave coolers have been needed since the late 1970's because these are better able to deal with the intense process heats now being generated in state-of-the-art, high stress furnaces. Copper stave coolers have also proved themselves capable of delivering furnace campaign lives that now exceed fifteen years.
The average thermal load levels a stave cooler will be subjected to depends on where it will be positioned within a blast furnace and how the furnace is operated. See FIG. 1. Cast-iron staves can still be successfully used in the less demanding middle and upper stack areas of blast furnaces, but the much higher average heat loads below in the lower stack, Belly, Bosh, Tuyere Level, and Hearth all require the use of higher performing, but more costly copper staves.
Cast iron staves are less efficient at cooling than are copper staves because the cast iron metal is relatively much lower in thermal conductivity. Their inherent thermal resistance allows heat to pile up too high if too much loading is presented. Poor internal bonding can add unnecessarily to the overall thermal resistance. Otherwise, cracks develop in the cast iron and the cracking can propagate into the steel pipes themselves. Cast iron staves have a de-bonding layer that adds to a thermal barrier between coolants circulating in its internal water-cooling tubes and the hot faces of the cast iron stave body. Both such effects conspire in reducing the overall heat transfer abilities of cast iron staves.
Such inefficiencies in cast iron stave heat transfer performance can overstress cast iron staves when hot face temperatures drive up over 700° C. Thermal deformations are hard to avoid. Cast iron stave bodies can also suffer phase-volume transformations when operated at very elevated temperatures. Fatigue cracking, stave body material spalling, and cooling pipes exposed directly to the furnace heat are common failures. Stave coolers can also be used in reduction vessels for the production of direct reduced iron (DRI).
A stave cooler is described by Todd Smith in United States Published Patent Application US-2015-0377554-A1, published Dec. 31, 2015. The Abstract reads,                A stave comprising an outer housing, an inner pipe circuit comprising individual pipes housed within the outer housing, wherein the individual pipes each has an inlet end and an outlet end and wherein each pipe may or may not be mechanically connected to another pipe, and a manifold, integral with or disposed on or in the housing; wherein the inlet and/or outlet ends of each individual pipe is disposed in or housed by the manifold. The manifold may be made of carbon steel while the housing may be made of copper.Todd Smith further adds, “Each of the inlet and outlet ends of each individual pipe may be surrounded in part by cast copper within a housing of the manifold.”        
When liquid-cooled stave coolers are disposed inside the steel containment shells of smelting furnaces, each conventional coolant connection must have a corresponding penetration or access window in the shell in order to complete the hose connections outside. And, conventionally, each stave cooler must be bolted to or otherwise mechanically attached to the steel containment shell to provide vertical support to itself and the refractory brick lining it supports and cools on its hot face.
The hot smelting inside the furnaces produces very hot, toxic, and often flammable process gases that will find escape paths between the refractory bricks, and between the stave coolers and out through any openings in the containment shell. So these penetration points must have good gas seals. One penetration is easier to seal and keep sealed than several. While two or more fixed points will lead to thermally induced mechanical stresses.
But because the stave coolers, containment shells, and refractory brick are all subject to thermal expansion forces, the gas seals can be compromised over the campaign years by constantly being worked back and forth. Stave coolers like those described by Todd Smith, have many independent circuits of coolant piping inside, and each produces pairs of coolant connection ends that must be passed out back and through the containment shell.
Todd Smith describes a “manifold” that can be made of carbon steel on the back of a housing that may be made of copper. He points out that his stave 100 provides for ease of installation since it reduces the number of access holes or apertures required in the furnace shell 51 necessary for the inlet/outlet piping 108 to and from 100 through furnace shell 51. And he says, that stave 100 is of very strong construction to provide much of the support necessary for installation of the stave 100 on furnace shell 51. The effects of stave expansion/contraction due to temperature changes in the furnace are minimized since individual pipe connections to furnace shell have been eliminated. And, stave 100 reduces weld breaches in pipe connections with furnace shell 51 since such connections have been eliminated. Todd Smith says further that his stave 100 reduces the importance/criticality of any support bolts needed to help support stave 100 on furnace shell 51 since such bolts are no longer relied upon to independently support stave 100 since manifold 106 carries much of the load required to support stave 100 on furnace shell 51.
A stave cooler that has one-only through-bulkhead neck that is always collared in an appropriate steel is needed in the industry to control process gas sealing and containment. All of the coolant piping from all the coolant circuits within a single rectangular copper body must pass through in a single tight group to then connect externally outside the steel containment shell. This minimizes the adverse effects of thermal expansion and contraction to manageable levels. Tightly grouping the individual pipe connections through the furnace shell limits the deteriorating forces at work.
Towards these ends, stave coolers must depend entirely for their vertical mechanical support by a single hanging of the through-bulkhead in a single corresponding penetration of the containment shell. Carrying only “much of the load” leaves the door open to more than one penetration of the steel containment shell per stave cooler. The two jobs of supporting the stave cooler's weight, and connecting all the coolant piping, must always be shared in a single through-bulkhead neck.